Critically ill patients are usually admitted with clinical and biochemical signs of systemic inflammation as a consequence of their disease. These signs are ascribed to the effects of inflammatory mediators produced during the early phase response to a stress of unspecified etiology. The systemic inflammatory response syndrome (SIRS) is the clinical response traditionally associated with this biological inflammation: its incidence can be more than 50% in critically ill patients, many of whom demonstrate or will develop severe infection (Brun-Buisson. Intensive Care Med. 2000; 26 Suppl 1:S64-74). C-reactive protein (CRP) and procalcitonin are the traditional biomarkers used to evaluate the level of biological inflammation during SIRS. Despite their sensitivity and specificity for the diagnosis of infection, neither procalcitonin nor CRP give significant information as to outcome in such patients (Harbarth et al. Am J Respir Crit. Care Med. 2001; 164:396-402), who often subsequently die with multiple organ failure. Most patients surviving initial hemodynamic failure experience an insidious, progressive decline of vital organ functions, corresponding to multiple organ failure (MOF), which is associated with high and short-term mortality rates. Mortality varies from 30% to 100% even in the absence of previous health disorders.
Attempts to characterise the severity of organ failures and to predict patient outcome is of major importance for physicians in the care of critically ill patients. From an historical point of view, score building was the first step to evaluate outcome in critically ill patients because previous attempts with biological parameters failed to succeed (Schetz et al. 2005; 28:1197-210). Several outcome prediction models have been developed and are currently available in intensive care unit management, such as the APACHE (Acute Physiology and Chronic Health Evaluation) (Knaus et al. Crit. Care Med. 1981; 9:591-597), SAPS (simplified acute physiology score) (Le Gall et al. JAMA 1993; 270: 2957-63), MPM (mortality probability models) (Lemeshow et al. Crit. Care Med. 1988; 16:470-477), SOFA (Sequential Organ Failure Assessment (SOFA) (Ferreira et al. JAMA 2001; 286: 1754-58), and LOD (Logistic Organ Dysfunction) (Timsit et al. Crit. Care Med 2002; 30: 2003-13). Among these approaches, SAPS is considered as the gold standard score.
However, these prediction models have several drawbacks. First of all, a calculation of score is generally only available 24 hours after Intensive care unit (ICU) admission. Generally, more than 10 parameters shall be evaluated for determining the score. Furthermore, these scores ignore the many factors that can influence patient outcome during the course of an ICU stay. Finally, it has been shown that these scoring systems are more useful to describe and quantify organ function than to predict a real outcome. Risk assessment of patients should be based on objective variables that can be routinely measured, like biological markers.